2 boiler oil/wood circulator controls

AmericanNYer

Hey thanks for the help everyone. I ultimately bought Primary Secondary Pumping Made Easy and it helped me with the planning of this project tremendously. Now I'm down to wiring the controls.

Oil boiler and Wood fired boiler each have their own dedicated pump connected to primary loop with closely spaced Ts.  Primary loop has its own dedicated pump. Three circuits each with their own pump.

I am looking to wire this so that the oil boiler and primary loop pump turn on along with whichever zone is calling. If the wood boiler is on I would like its pump to turn on when high limit reached on aquastat, the primary pump to turn on, and all zones to turn on - all pumps on except for the oil boiler.

Any control/wiring recommendations or other advice?

Thanks again. 

hot_rod

So the wood boiler as a back up? Does the oil boiler shut off whenever the wood boiler is hot enough?

AmericanNYer

Yes, if the wood boiler is on I would like the oil boiler to be off. If the wood boiler burns out I would like the oil boiler to automatically be able to fire back up

hot_rod

So the oil boiler and circ turns on via a thermostat call? Wired through a relay box?

I use differential controls, aka solar controller, aka ∆T controller.
These come with two sensors. So you can watch and respond to two conditions.
Sensor 1, S-1 would go on top of the wood boiler somewhere. S2 on the pipe above the oil boiler. So whenever S1 is warmer then S2 by say 8° P2, the wood boiler circ kicks on. Wired through a RIB relay, it also drops the call to the oil boiler TT.

When the wood boiler temperature drops 8° P2 stops, and the call goes back to the oil.
Additionally you set a minimum on the wood boiler, so it would not kick on until above 150 or so to prevent condensing conditions.
Those on/ off differentials are adjustable, and there are some other features like variable speed setting. That modulates P2 speed based on the what the boiler can provide, speeds up as temperature rises, slows down as the fire goes low.

Do you need overheat protection for the wood boiler? If the heat calls ends and the wood boiler is fired what is the control logic? A dump zone perhaps?

Adding a 3rd sensor to the control could activate relay 2 in the controller to dump or fire up one of the zone circs. Maybe if the wood boiler reaches 190 a dump activates.

Typically we have the wood boiler as priority, oil kicks on if the wood cannot keep up. Is there a DHW function in the mix?

Here is a piping example.

AmericanNYer

Appreciate your time in helping me with this. I am in planning phase, about to start laying the pipe. So right now there are no controls installed. Here is the plan. 

hot_rod

It can be tricky to manage a wood fired boiler without some amount of buffer tank. You need to adjust the firing of the boiler to constantly match the heat load of the building. If you load the firebox and walk away, they tend to overheat

Your piping example is a series primary loop. The piping drawing I attached up a few posts is also primary secondary, but without a looo and that additional circulator. Also the loads are parallel so every zone sees the same temperature. In your example each load sees a lower temperature as return temperature blends down the supply to the next set of tees

The method I showed eliminates a pump, less piping, better control of the distribution

Control logic is about the same, wood boiler is the lead, oil only fires when temperature drops in the wood boiler below a selected temperature, maybe 150- 160. Depending on how hot if supply your heat emitters need

google Caleffi Idronics and download the issue on wood boilers, number 10 I think.

AmericanNYer

Thanks again for your time with this.  On the system you recommended to me in your drawing, the expansion tank is at the end of the return side of the main line. How would I incorporate the air eliminator, which would have the tank mounted below, since water would not be actively pumping through that portion. 

hot_rod

Here are a few piping versions of this parallel primary loop.
The key to this is the "horseshoe"loop, or "moose antler" header, is the piping size needs to be large. Ideally sized to handle every load and input operating at once with low flow velocity in that pipe.
As such the expansion tank provided the PONPC for each circulator through that low flow resistance pipe.

I'd like to see a air separator on each boiler right at the supply connection. That grabs the air at the very best point.

It could be a single purger in the loop also, just upstream of the circ connections.

EdTheHeaterMan

Check your work.
you may want to install the hot feed to the radiators before the return from the radiators.
Unless you are just going to put arrows inside the pipes before you put them together, so the water knows which way to go. Hot water is just like electric, it's colorblind and won't know which pipe to go in just by the color on your diagram

hot_rod

just know with a circle primary loop like that you have temperature drop to account for. If your various loads are looking for the same SWT, it's not going to happen. Without a more complex loop with balanced crossovers, fig. 5-9.

Here is the math for calculating series drop temperatures.